From: ebiederm@xmission.com (Eric W. Biederman)
To: Oleg Nesterov <oleg@redhat.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
Andrew Morton <akpm@linux-foundation.org>,
Kees Cook <keescook@chromium.org>,
David Howells <dhowells@redhat.com>,
linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Rik van Riel <riel@redhat.com>,
Vladimir Davydov <vdavydov@parallels.com>,
Ricky Zhou <rickyz@chromium.org>, Julien Tinnes <jln@google.com>
Subject: Re: [PATCH v2] unshare: Unsharing a thread does not require unsharing a vm
Date: Thu, 13 Aug 2015 11:39:51 -0500 [thread overview]
Message-ID: <877fozta5k.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <20150813163025.GA24027@redhat.com> (Oleg Nesterov's message of "Thu, 13 Aug 2015 18:30:25 +0200")
Oleg Nesterov <oleg@redhat.com> writes:
> On 08/13, Eric W. Biederman wrote:
>>
>> Oleg Nesterov <oleg@redhat.com> writes:
>>
>> > On 08/12, Eric W. Biederman wrote:
>> >>
>> >> + if (unshare_flags & (CLONE_SIGHAND | CLONE_VM)) {
>> >> + if (atomic_read(¤t->sighand->count) > 1)
>> >> + return -EINVAL;
>> >> + }
>> >
>> > I am still not sure we want this... please the the previous email.
>>
>> Reading your other email I did not see why you thought this check was
>> unnecessary.
>>
>> > But perhaps I missed something.
>>
>> In short:
>> clone(VM) --> mm_users > 1 && sighand_struct->count == 1
>> followed by:
>> unshare(SIGHAND)
>> the unshare should succeed.
>>
>> Meanwhile:
>> clone(VM|SIGHAND) --> mm_users > 1 && sighand_struct->count > 1
>> followed by:
>> unshare(SIGHAND)
>> the unshare should fail.
>
> Yes, yes, yes.
>
> But once again, I meant we can remove this sighand->count check
> if unshare(SIGHAND) checks current_is_single_threaded(). That is
> why I suggested to do
>
> if (unshare_flags & CLONE_SIGHAND)
> unshare_flags |= CLONE_VM;
>
> in sys_unshare(), or change check_unshare_flags() to check
> "unshare_flags & (CLONE_VM | CLONE_SIGHAND)" before
> current_is_single_threaded().
See the two cases above that change to unshare_flags will make
unshare(SIGHAND) fail when sighand_struct->count == 1.
Which is fundamentally wrong.
> Damn. And this discussion makes me think that another cleanup makes
> sense too. Can't we move all these unshare_flags manipulations into
> check_unshare_flags? So that sys_unshare() will only do
>
> err = check_unshare_flags(&unshare_flags);
>
> and the reader of this code won't need to read 2 functions to understand
> whats going on.
Eric
next prev parent reply other threads:[~2015-08-13 16:46 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-28 17:15 [PATCH] user_ns: use correct check for single-threadedness Kees Cook
2015-07-28 18:02 ` Rik van Riel
2015-07-28 18:17 ` Eric W. Biederman
2015-07-28 20:55 ` Ricky Zhou
2015-07-28 21:01 ` Kees Cook
2015-08-05 18:13 ` Eric W. Biederman
2015-08-05 19:40 ` Kees Cook
2015-07-28 21:35 ` Andrew Morton
2015-07-28 21:50 ` Kees Cook
2015-07-28 22:11 ` Kirill A. Shutemov
2015-08-05 11:38 ` Ingo Molnar
2015-08-05 11:53 ` Kirill A. Shutemov
2015-08-05 13:13 ` Ricky Zhou
2015-08-05 17:23 ` Oleg Nesterov
2015-08-05 18:00 ` Eric W. Biederman
2015-08-05 18:52 ` Eric W. Biederman
2015-08-06 13:06 ` Oleg Nesterov
2015-08-06 13:44 ` Oleg Nesterov
2015-08-12 1:17 ` Eric W. Biederman
2015-08-12 14:40 ` Oleg Nesterov
2015-08-12 15:11 ` Eric W. Biederman
2015-08-12 1:22 ` [PATCH 0/2] userns: Creation logic fixes Eric W. Biederman
2015-08-12 1:24 ` [PATCH 1/2] unshare: Unsharing a thread does not require unsharing a vm Eric W. Biederman
2015-08-12 17:48 ` Oleg Nesterov
2015-08-12 18:39 ` Eric W. Biederman
2015-08-13 12:55 ` Oleg Nesterov
2015-08-13 15:38 ` Eric W. Biederman
2015-08-13 16:17 ` Oleg Nesterov
2015-08-13 16:27 ` Eric W. Biederman
2015-08-13 16:50 ` Oleg Nesterov
2015-08-14 17:59 ` Oleg Nesterov
2015-08-12 19:59 ` [PATCH v2] " Eric W. Biederman
2015-08-13 12:57 ` Oleg Nesterov
2015-08-13 16:01 ` Eric W. Biederman
2015-08-13 16:30 ` Oleg Nesterov
2015-08-13 16:39 ` Eric W. Biederman [this message]
2015-08-12 1:25 ` [PATCH 2/2] userns,pidns: Force thread group sharing, not signal handler sharing Eric W. Biederman
2015-08-12 17:24 ` Oleg Nesterov
2015-08-12 6:29 ` [PATCH 0/2] userns: Creation logic fixes Kees Cook
2015-08-06 14:35 ` [PATCH] user_ns: use correct check for single-threadedness Oleg Nesterov
2015-08-06 21:16 ` Eric W. Biederman
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